This invention relates to a detection system which displays conditions of the surrounding area to be observed, and a radial reference marker, on the face of a cathode-ray tube in a form of plan position indication. More particularly, it relates to an indicating apparatus of the detection system which can display a radial reference marker in any direction on the face of the cathode-ray tube.
A detection system transmits search pulses from a transmitting and receiving unit rotated at constant speed in synchronism with the rotation of a deflection coil around the neck of a cathode-ray tube, and supplies received echo signals and a bearing signal generated when the transmitting and receiving unit points in a predetermined direction for the intensity control input of the cathode-ray tube. The deflection coil is adapted to successively deflect the electron beam to make radial sweeps in different directions one after another over the screen of the cathode-ray tube in synchronism with each transmission of a search pulse. Hence, the cathode-ray tube displays bright spots at corresponding places and a radial bright line in a corresponding direction thereover. The indicating apparatus of the detection system controls the advance or delay of the phase of the deflection coil with respect to that of the transmitting and receiving unit by increasing or decreasing the rotating speed of the deflection coil, so that a reference marker can be displayed in any direction.
The invention has particular application in radar systems which rotate the deflection coil of a cathode-ray tube at constant speed in synchronism with the rotation of the antenna scanner, and change, if necessary, the rotating speed of the deflection coil with respect to that of the antenna scanner by utilizing bearing signals supplied from a gyro compass. It can also be applied in the sonar class devices which have a rotatable transmitting and receiving ultrasonic transducer, and a cathode-ray tube around the neck of which a deflection coil is mounted and rotated in synchronism with the rotation of the ultrasonic transducer.
Hereinafter, the invention will be explained as embodied in a shipborne radar system although as explained above the invention is not limited to that particular system.
In an indicating apparatus of a ship mounted radar system, such well-known methods of presenting an image of the surrounding area to be observed over the face of a cathode-ray tube have been proposed as, for example: (1) relative display in "Ship's head up", (2) stabilized display in "North-up stabilized" and (3) stabilized display in "Ship's head up". With a relative display in "Ship's head up", a heading marker showing the direction of a ship's head always points upward (0.degree.). When the ship changes its course, the image turns but the heading marker remains in the same position pointing in the direction of 0.degree. on the scale fixed around the periphery of the face of a cathode-ray tube. The deflection coil of the cathode-ray tube is made to rotate in synchronism with the antenna scanner. With a stabilized display in "North-up stabilized", the picture of the area represented remains in the same position, irrespective of any changes of course by the ship, but the heading marker moves accordingly in a clockwise or an anti-clockwise direction. The deflection coil of the cathode-ray tube is controlled to change its phase relationship with the antenna scanner by utilizing bearing signals supplied from a gyro compass. A true bearing of the ship's head can be read from the heading marker and the fixed scale. With a stabilized display in "Ship's head up", the picture of the area remains in the same position but the heading marker moves with the yawing of the ship. Bearing signals produced from a gyro compass are also utilized to change the rotating speed of the deflection coil with respect to the antenna, thereby moving only the heading marker. A relative bearing of the ship's head with respect to the direction the ship was proceeding when switched to the stabilized display in "Ship's head up" can be read from the heading marker and the fixed scale.
In a prior art indicating apparatus of a radar equipment, a servomechanism has been utilized to rotate the deflection coil of a cathode-ray tube in synchronism with the rotation of the antenna and to control the amount of the phase difference between the two rotating members, thus presenting both a relative display in "Ship's head up" and a stabilized display in "North-up". Such an apparatus, however, cannot present a stabilized display in "Ship's head up" in addition to the other two methods of display, and moreover requires a synchro transmitter, a synchro receiver, a synchro differential transmitter and a servomotor, thus making the apparatus bulky and costly.